I. Field
The following description relates generally to wireless communication systems and more particularly to transmission of inter-sector control channels.
II. Background
Wireless communication systems are deployed to provide a multitude of communication services such as voice, video, packet data, broadcast, and messaging services as well as others. These systems can be multiple-access systems capable of supporting communication for a number of terminals by sharing available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, as well as other systems.
Wireless multiple-access communication systems can simultaneously support communication for multiple wireless terminals. In such systems, each terminal can communicate with one or more sectors through transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the sectors to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the sectors. These communication links can be established through a single-in-single-out (SISO), multiple-in-single-out (MISO), and/or multiple-in-multiple-out (MIMO) systems.
Multiple terminals can simultaneously transmit on the reverse link by multiplexing their transmissions to be orthogonal to one another in the time, frequency, and/or code domain. If complete orthogonality between transmissions is achieved, transmissions from each terminal do not interfere with transmissions from other terminals at a receiving sector. However, complete orthogonality among transmissions from different terminals is often not realized due to channel conditions, receiver imperfections, as well as other factors (e.g. overhead/difficulty of a frequency planned reuse). As a result, terminals often cause some amount of interference to other terminals. Furthermore, because transmissions from terminals communicating with different sectors are typically not orthogonal to one another, each terminal can also cause interference to terminals communicating with nearby sectors. This leads to a need to control the interference caused at a base station by terminals in other sectors.
In some systems, the entire allocated channel bandwidth is utilized in every sector, which is referred to as a frequency reuse of one. Frequency reuse indicates the rate at which the same frequency can be used in the network. A frequency reuse of one creates a challenge for inter-sector control messages that target users in adjacent sectors. These control messages can be interference control messages, handoff messages, and/or other messages. A frequency reuse of one can provide a low signal-to-interference ratio (SIR), such as −15 dB, −20 dB, −30 db, or lower, for example; particularly for users in adjacent sectors. However, the data might only be received by a subset of all mobile devices that should have the information (e.g. edge devices, devices close to the adjacent sector transmitting base station), since the serving sector base station received power is much greater than the adjacent sector base station received power due to the closer RF proximity. This creates a challenge for transmitting control messages to users in adjacent sectors. If, for example, users in adjacent sectors are creating too much interference on the reverse link of a specific base station, then that base station may want to signal to users to backoff their transmit powers. However, with a reuse of one, only the edge users in the adjacent sector may be able to receive the power backoff control message since users deeper into the sector will experience too much interference from their serving base station. The edge mobile devices that receive the data might overcompensate for devices that do not receive the message, further the users that do not receive the message may continue transmitting at a power level that causes too much interference to adjacent sectors. Thus, performance and coverage relating to control messages might be less than ideal.
In conventional systems, an other-sector control message can be utilized to transmit interference information (e.g., amount of interference), as well as for other purposes, including handoff, inter-sector power control for managing inter-sector interference, sector loading, or other control messages. A traditional approach is to transmit the control message from each sector and target a very low spectral efficiency such that the message is decodable at very low signal to noise ratio (SNR) in the adjacent sector. Spectral efficiency is the amount of information that can be transmitted over a given bandwidth and is a measure of how efficiently a limited frequency spectrum is utilized. This results in utilizing a lot of system resources for these other sector control messages that still do not reach all the way into the adjacent sectors. Thus, there is a need in the art for an other sector control transmission technique that utilizes less resources and can target users deep into adjacent sectors.